Power transmission belts are known in which the gum is made of a polybutadiene and chloroprene material (also known as polybutadiene rubber/chloroprene rubber or (BR/CR)).
That material is capable of satisfying some of the above-mentioned constraints, in particular mechanical constraints and acoustic constraints.
Nevertheless, that material does not behave well at high temperatures.
Too great a temperature constraint leads to bakelization of the belt which can no longer operate correctly.
Power transmission belts are known in which the teeth are made out of an ethylene-propylene-diene-monomer (EPDM) material. This applies for example to patent application FR 2 779 731 where the belt also has cords.
That material, unlike the BR/CR material, presents good high temperature properties.
Nevertheless, it presents a coefficient of friction with pulleys that is relatively high. Unfortunately, a high coefficient of friction can lead to high levels of shear stress at the interface between the gum and the cords. These stresses can thus lead to the cords being torn out, or sometimes to the teeth being torn off.
Furthermore, too high a coefficient of friction can lead to a level of (acoustic) noise that does not comply with the ever stricter requirements being imposed by clients.
Numerous solutions have thus been sought to deal with these problems of cords being torn out and of noise on belts having teeth made of a material based on EPDM.
For this purpose, Documents FR 2 898 171 and FR 2 936 291 propose adding a protective film on the outer surface of the teeth that might be made of EPDM, which film is for coming into contact with the pulleys.
More precisely, application FR 2 898 171 shows the presence of a thermoplastic film containing polyethylene. Nevertheless, in certain situations of high thermomechanical stresses, the film can abrade quickly and thus no longer perform its function.
In application FR 2 936 291, the protective film has a barrier layer made of thermoplastic and an outer coating, e.g. made of polyethylene that is partially included in the thermoplastic barrier layer. That solution is complex to implement and expensive.
There therefore exists a need for a power transmission belt that presents excellent performance for satisfying the mechanical and/or thermal and/or acoustic constraints that are now being required.